Atoms form ions in order to gain positivity or negativity. Ions are groups of atoms that generally have a net electrical charge, and are formed when protons or electrons are gained or lost by an atom.
Every atom has a nucleus, which is made up of neutrons and protons. The nucleus is surrounded by electrons that are arranged around it in several orbits, or shells. Each orbit can only host a specific density of electrons known as an orbital. The lower-most shell, or first shell, has an s-orbital, which contains only two electrons. The next shell has an s-orbital, which is made up of two electrons and a p-orbital that has six electrons. Then the third shell consists of eight electrons, and so on.
If the outermost shell is not made up of eight electrons, the atom can accept or give away electrons to make it have a total of eight electrons. If an atom has the tendency to give away electrons, it attains positivity. The positivity of an atom is normally represented by a positive ion. If an atom has a tendency to accept electrons, it gains a negative charge. The negativity is represented by a negative ion.
A neutral atom has an equal number of electrons and protons, so it does not have a net electrical charge.